1. Field of the Invention
The present invention generally relates to an image detection apparatus, and more particularly to a type of image detection apparatus having a line type optical sensor with an alignment of light receiving elements and using internal scattered light scattered inside a finger tip and emitted from a surface of the finger for obtaining a fingerprint by sliding the finger thereacross.
2. Description of the Related Art
In recent years, electronic apparatuses such as a computer, and portable communication apparatuses such a mobile phone are mounted with an image detection apparatus such as a fingerprint sensor, which identifies fingerprints on a finger for individual identification, from the aspect of security. Here, the fingerprint sensor is desired to provide a satisfactory reliability at a low manufacture cost, and to have a small size for allowing assembly to a small-sized apparatus such as a mobile communication apparatus.
As one image detection apparatus, there is an optical type fingerprint sensor. The optical type fingerprint sensor can be classified into a type which utilizes light reflected from a surface of a finger, as shown in FIG. 11(A), and another type which utilizes internal scattered light that scatters in the finger and is emitted from the surface of the finger. Numeral 1 indicates a finger including a finger tip, numeral 2 indicates a glass plate, numeral 3 indicates a light emitting diode serving as a lighting source, numeral 4 indicates an optical sensor, numeral 10 indicates a projection light, and numeral 11 indicates a reflected light reflected from a surface of a finger. Numeral 12 indicates an internal scattered light. With the type utilizing reflected light, there is a fluctuation in the quality of the obtained fingerprint image depending on whether the finger is in a moist state or a dry state. Accordingly, this type employs complicated image processing and uses a specialized processor in order to obtain an image quality for enabling fingerprint authentication. It is, therefore, difficult to reduce manufacture cost to a low cost. With the type utilizing internal scattered light, a fingerprint image of a satisfactory quality can be obtained regardless of whether the finger is in a moist or dry state. Accordingly, image processing can be simple, and a typical processor can be sufficient for this type. Therefore, manufacture cost can be reduced to a low cost. It is to be noted that the refractive index of the finger is approximately 1.5 to 1.7.
An example of a conventional fingerprint sensor of the type utilizing the internal scattered light is shown in U.S. Pat. No. 4,932,776. This fingerprint sensor, however, is of a large size, and is difficult to be assembled to a small-sized apparatus such as a portable communication apparatus. One reason causing this difficulty is that an optical source is situated at a position in a light guide member facing a surface to which a finger is contacted, and is disposed apart from the surface. Another reason is that the optical sensor chip is an area type optical sensor chip having light receiving elements aligned in a matrix form, and that the light guide member has a cross-section that corresponds to the size of a fingertip.